[confighttp] Remove pointers from integer fields (#12323)

<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
#### Description

I was looking through our defaults for a few `confighttp.ClientConfig`
fields and found that `0` disables these fields in the underlying
`http.Transport` object, which means we don't need them to be pointers.

Docs for the four fields we set in `http.Transport` here:
https://pkg.go.dev/net/http#Transport.MaxIdleConns

I also stopped assigning defaults to any fields we take from
`http.DefaultTransport` where setting them is a no-op since they aren't
set in `http.DefaultTransport`.

<!-- Issue number if applicable -->
#### Link to tracking issue

Helps unblock confighttp 1.0 from depending on
#9478

.chloggen/confighttp-remove-pointers.yaml

@@ -0,0 +1,25 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: breaking
+
+# The name of the component, or a single word describing the area of concern, (e.g. otlpreceiver)
+component: confighttp
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Make the client config options `max_idle_conns`, `max_idle_conns_per_host`, `max_conns_per_host`, and `idle_conn_timeout` integers
+
+# One or more tracking issues or pull requests related to the change
+issues: [9478]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext: All four options can be set to `0` where they were previously set to `null`
+
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: [user]

config/confighttp/confighttp.go

@@ -77,21 +77,20 @@ type ClientConfig struct {
 	CompressionParams configcompression.CompressionParams `mapstructure:"compression_params"`
 
 	// MaxIdleConns is used to set a limit to the maximum idle HTTP connections the client can keep open.
-	// By default, it is set to 100.
-	MaxIdleConns *int `mapstructure:"max_idle_conns"`
+	// By default, it is set to 100. Zero means no limit.
+	MaxIdleConns int `mapstructure:"max_idle_conns"`
 
 	// MaxIdleConnsPerHost is used to set a limit to the maximum idle HTTP connections the host can keep open.
-	// By default, it is set to [http.DefaultTransport.MaxIdleConnsPerHost].
-	MaxIdleConnsPerHost *int `mapstructure:"max_idle_conns_per_host"`
+	// Default is 0 (unlimited).
+	MaxIdleConnsPerHost int `mapstructure:"max_idle_conns_per_host"`
 
 	// MaxConnsPerHost limits the total number of connections per host, including connections in the dialing,
-	// active, and idle states.
-	// By default, it is set to [http.DefaultTransport.MaxConnsPerHost].
-	MaxConnsPerHost *int `mapstructure:"max_conns_per_host"`
+	// active, and idle states. Default is 0 (unlimited).
+	MaxConnsPerHost int `mapstructure:"max_conns_per_host"`
 
 	// IdleConnTimeout is the maximum amount of time a connection will remain open before closing itself.
-	// By default, it is set to [http.DefaultTransport.IdleConnTimeout]
-	IdleConnTimeout *time.Duration `mapstructure:"idle_conn_timeout"`
+	// By default, it is set to 90 seconds.
+	IdleConnTimeout time.Duration `mapstructure:"idle_conn_timeout"`
 
 	// DisableKeepAlives, if true, disables HTTP keep-alives and will only use the connection to the server
 	// for a single HTTP request.
@@ -129,13 +128,9 @@ func NewDefaultClientConfig() ClientConfig {
 	defaultTransport := http.DefaultTransport.(*http.Transport)
 
 	return ClientConfig{
-		ReadBufferSize:      defaultTransport.ReadBufferSize,
-		WriteBufferSize:     defaultTransport.WriteBufferSize,
-		Headers:             map[string]configopaque.String{},
-		MaxIdleConns:        &defaultTransport.MaxIdleConns,
-		MaxIdleConnsPerHost: &defaultTransport.MaxIdleConnsPerHost,
-		MaxConnsPerHost:     &defaultTransport.MaxConnsPerHost,
-		IdleConnTimeout:     &defaultTransport.IdleConnTimeout,
+		Headers:         map[string]configopaque.String{},
+		MaxIdleConns:    defaultTransport.MaxIdleConns,
+		IdleConnTimeout: defaultTransport.IdleConnTimeout,
 	}
 }
 
@@ -172,21 +167,10 @@ func (hcs *ClientConfig) ToClient(ctx context.Context, host component.Host, sett
 		transport.WriteBufferSize = hcs.WriteBufferSize
 	}
 
-	if hcs.MaxIdleConns != nil {
-		transport.MaxIdleConns = *hcs.MaxIdleConns
-	}
-
-	if hcs.MaxIdleConnsPerHost != nil {
-		transport.MaxIdleConnsPerHost = *hcs.MaxIdleConnsPerHost
-	}
-
-	if hcs.MaxConnsPerHost != nil {
-		transport.MaxConnsPerHost = *hcs.MaxConnsPerHost
-	}
-
-	if hcs.IdleConnTimeout != nil {
-		transport.IdleConnTimeout = *hcs.IdleConnTimeout
-	}
+	transport.MaxIdleConns = hcs.MaxIdleConns
+	transport.MaxIdleConnsPerHost = hcs.MaxIdleConnsPerHost
+	transport.MaxConnsPerHost = hcs.MaxConnsPerHost
+	transport.IdleConnTimeout = hcs.IdleConnTimeout
 
 	// Setting the Proxy URL
 	if hcs.ProxyURL != "" {

config/confighttp/confighttp_test.go

@@ -77,10 +77,10 @@ func TestAllHTTPClientSettings(t *testing.T) {
 				},
 				ReadBufferSize:       1024,
 				WriteBufferSize:      512,
-				MaxIdleConns:         &maxIdleConns,
-				MaxIdleConnsPerHost:  &maxIdleConnsPerHost,
-				MaxConnsPerHost:      &maxConnsPerHost,
-				IdleConnTimeout:      &idleConnTimeout,
+				MaxIdleConns:         maxIdleConns,
+				MaxIdleConnsPerHost:  maxIdleConnsPerHost,
+				MaxConnsPerHost:      maxConnsPerHost,
+				IdleConnTimeout:      idleConnTimeout,
 				Compression:          "",
 				DisableKeepAlives:    true,
 				Cookies:              &CookiesConfig{Enabled: true},
@@ -98,10 +98,10 @@ func TestAllHTTPClientSettings(t *testing.T) {
 				},
 				ReadBufferSize:       1024,
 				WriteBufferSize:      512,
-				MaxIdleConns:         &maxIdleConns,
-				MaxIdleConnsPerHost:  &maxIdleConnsPerHost,
-				MaxConnsPerHost:      &maxConnsPerHost,
-				IdleConnTimeout:      &idleConnTimeout,
+				MaxIdleConns:         maxIdleConns,
+				MaxIdleConnsPerHost:  maxIdleConnsPerHost,
+				MaxConnsPerHost:      maxConnsPerHost,
+				IdleConnTimeout:      idleConnTimeout,
 				Compression:          "none",
 				DisableKeepAlives:    true,
 				HTTP2ReadIdleTimeout: idleConnTimeout,
@@ -118,10 +118,10 @@ func TestAllHTTPClientSettings(t *testing.T) {
 				},
 				ReadBufferSize:       1024,
 				WriteBufferSize:      512,
-				MaxIdleConns:         &maxIdleConns,
-				MaxIdleConnsPerHost:  &maxIdleConnsPerHost,
-				MaxConnsPerHost:      &maxConnsPerHost,
-				IdleConnTimeout:      &idleConnTimeout,
+				MaxIdleConns:         maxIdleConns,
+				MaxIdleConnsPerHost:  maxIdleConnsPerHost,
+				MaxConnsPerHost:      maxConnsPerHost,
+				IdleConnTimeout:      idleConnTimeout,
 				Compression:          "gzip",
 				DisableKeepAlives:    true,
 				HTTP2ReadIdleTimeout: idleConnTimeout,
@@ -138,10 +138,10 @@ func TestAllHTTPClientSettings(t *testing.T) {
 				},
 				ReadBufferSize:       1024,
 				WriteBufferSize:      512,
-				MaxIdleConns:         &maxIdleConns,
-				MaxIdleConnsPerHost:  &maxIdleConnsPerHost,
-				MaxConnsPerHost:      &maxConnsPerHost,
-				IdleConnTimeout:      &idleConnTimeout,
+				MaxIdleConns:         maxIdleConns,
+				MaxIdleConnsPerHost:  maxIdleConnsPerHost,
+				MaxConnsPerHost:      maxConnsPerHost,
+				IdleConnTimeout:      idleConnTimeout,
 				Compression:          "gzip",
 				DisableKeepAlives:    true,
 				HTTP2ReadIdleTimeout: idleConnTimeout,
@@ -212,19 +212,19 @@ func TestPartialHTTPClientSettings(t *testing.T) {
 			transport := client.Transport.(*http.Transport)
 			assert.EqualValues(t, 1024, transport.ReadBufferSize)
 			assert.EqualValues(t, 512, transport.WriteBufferSize)
-			assert.EqualValues(t, 100, transport.MaxIdleConns)
+			assert.EqualValues(t, 0, transport.MaxIdleConns)
 			assert.EqualValues(t, 0, transport.MaxIdleConnsPerHost)
 			assert.EqualValues(t, 0, transport.MaxConnsPerHost)
-			assert.EqualValues(t, 90*time.Second, transport.IdleConnTimeout)
+			assert.EqualValues(t, 0, transport.IdleConnTimeout)
 			assert.False(t, transport.DisableKeepAlives)
 		})
 	}
 }
 
 func TestDefaultHTTPClientSettings(t *testing.T) {
 	httpClientSettings := NewDefaultClientConfig()
-	assert.EqualValues(t, 100, *httpClientSettings.MaxIdleConns)
-	assert.EqualValues(t, 90*time.Second, *httpClientSettings.IdleConnTimeout)
+	assert.EqualValues(t, 100, httpClientSettings.MaxIdleConns)
+	assert.EqualValues(t, 90*time.Second, httpClientSettings.IdleConnTimeout)
 }
 
 func TestProxyURL(t *testing.T) {
@@ -1027,6 +1027,41 @@ func TestHttpClientHostHeader(t *testing.T) {
 	})
 }
 
+func TestHttpTransportOptions(t *testing.T) {
+	settings := componenttest.NewNopTelemetrySettings()
+	// Disable OTel instrumentation so the *http.Transport object is directly accessible
+	settings.MeterProvider = nil
+	settings.TracerProvider = nil
+
+	clientConfig := NewDefaultClientConfig()
+	clientConfig.MaxIdleConns = 100
+	clientConfig.IdleConnTimeout = time.Duration(100)
+	clientConfig.MaxConnsPerHost = 100
+	clientConfig.MaxIdleConnsPerHost = 100
+	client, err := clientConfig.ToClient(context.Background(), &mockHost{}, settings)
+	require.NoError(t, err)
+	transport, ok := client.Transport.(*http.Transport)
+	require.True(t, ok, "client.Transport is not an *http.Transport")
+	require.Equal(t, 100, transport.MaxIdleConns)
+	require.Equal(t, time.Duration(100), transport.IdleConnTimeout)
+	require.Equal(t, 100, transport.MaxConnsPerHost)
+	require.Equal(t, 100, transport.MaxIdleConnsPerHost)
+
+	clientConfig = NewDefaultClientConfig()
+	clientConfig.MaxIdleConns = 0
+	clientConfig.IdleConnTimeout = 0
+	clientConfig.MaxConnsPerHost = 0
+	clientConfig.IdleConnTimeout = time.Duration(0)
+	client, err = clientConfig.ToClient(context.Background(), &mockHost{}, settings)
+	require.NoError(t, err)
+	transport, ok = client.Transport.(*http.Transport)
+	require.True(t, ok, "client.Transport is not an *http.Transport")
+	require.Equal(t, 0, transport.MaxIdleConns)
+	require.Equal(t, time.Duration(0), transport.IdleConnTimeout)
+	require.Equal(t, 0, transport.MaxConnsPerHost)
+	require.Equal(t, 0, transport.MaxIdleConnsPerHost)
+}
+
 func TestContextWithClient(t *testing.T) {
 	testCases := []struct {
 		name       string

exporter/otlphttpexporter/config_test.go

@@ -77,10 +77,10 @@ func TestUnmarshalConfig(t *testing.T) {
 				WriteBufferSize:     345,
 				Timeout:             time.Second * 10,
 				Compression:         "gzip",
-				MaxIdleConns:        &defaultMaxIdleConns,
-				MaxIdleConnsPerHost: &defaultMaxIdleConnsPerHost,
-				MaxConnsPerHost:     &defaultMaxConnsPerHost,
-				IdleConnTimeout:     &defaultIdleConnTimeout,
+				MaxIdleConns:        defaultMaxIdleConns,
+				MaxIdleConnsPerHost: defaultMaxIdleConnsPerHost,
+				MaxConnsPerHost:     defaultMaxConnsPerHost,
+				IdleConnTimeout:     defaultIdleConnTimeout,
 			},
 		}, cfg)
 }